The present disclosure relates to an image reading device that includes document placement portions on which documents are placed and a document feed portion referred to as so-called ADF, an image forming apparatus including the image reading device, and an image reading method for reading an image of a document by the image reading device.
An image reading device is known which includes a detection sensor that detects the size of a document that is set on a document feed portion that feeds documents and is referred to as so-called ADF. In addition, as this type of image reading device, an image reading device of a type is also known which is not provided with a detection sensor that detects the size of a document placed on a document placement portion that is formed of a glass plate or the like. In such an image reading device, when causing the image reading device to read an image of a document placed on the document placement portion, a user needs to notify the image reading device of the size of the document. Here, the user may notify the image reading device of the size of the document by performing an input operation such as looking for and pressing an operation button corresponding to the size of the document, which is a reading target, among a plurality of operation buttons that are provided on an operation panel so as to correspond to a plurality of document sizes, respectively. As conventional art, an image forming apparatus is known which includes a scanner that does not include a detection sensor that detects the size of a document.